Yes, now it does. Silica gel comes in either non-indicating or self-indicating forms. Non indicating silica gel is white and stays white as it adsorbs moisture. Self-indicating silica gel have traditionally been impregnated with a moisture sensitive cobalt chloride indicator. This gives a blue silica gel which slowly changes colour as it adsorbs moisture until it becomes pink. New self-indicating silica gel feature a number of other colours (because they have different moisture sensitive indicators), but all have the same purpose - to indicate when the silica gel is saturated and unable to take up any more moisture.
Yes. The silica gel does not need to be 'generated' before use. It is always sold (loose or in sachets) in a dry condition, ready for use.
Almost indefinitely. The key to retaining sachets usefulness is to keep it under air tight conditions until it needs to be used. Silica gel will absorb moisture from any environment, so a sachet left out in the open will immediately start taking up water vapour. Although the moisture uptake rate is not fast, small sachets can be vulnerable to such exposure, as they do not have a large moisture holding capacity. It is recommended that they are not left open to the atmosphere for longer than 15 minutes. Larger sachets should not be removed from their packaging more than 1 hour before they are required for use. The shelf life of silica gel in a sealed environment can safely be said to be between 4 and 12 months. Practical experience has shown that it can often far exceed this.
Silica gel will adsorb up to 40% of its own weight in moisture.
Theoretically yes, but it is really only effective in an enclosed environment. In a situation where new air (and moisture) is constantly being introduced, an unpractical amount of silica gel will likely be needed to keep the Relative Humidity at low levels.
Air will always contain water vapour. At any given temperature there will be a saturation point at which no more moisture can be retained (any excess will condense). The Relative Humidity of air is the actual moisture content expressed as a percentage of this saturation content. The aim of using silica gel is to keep the Relative Humidity at levels below 50% of the saturation capacity. At these levels, corrosion and mould growth will not be promoted. Problems are often caused if the temperature drops as the saturation content of air at the new temperature becomes much lower.
Non-indicating (white) silica gel is non-toxic and non-flammable, it is very inert with a very high melting point. It is very much like sand and thus can safely be sent by any means of transport. Self-indicating (blue) silica gel has been reclassified by the European Union and as of 01/07/2000 is classified as toxic. More here. New safe self-indicating silica gel are now available.
The materials used to make silica gel sachets are specifically chosen to be breathable. Water vapour passes through them to be adsorbed by the silica gel.
The larger the item that is being protected, the more silica gel is needed. A range of sachets allows for a single sachet to be used in most cases.
It will depend on the application. For a well sealed item, a rule of thumb is that 5 grams of silica gel are needed for every cubic foot of volume of the package. This converts to 170 grams per cubic meter.
Yes. The blue - self-indicating silica gel can be seen through the sachet material.
There are two methods used for re-drying silica gel. One method uses the oven, and the other uses the microwave. Before you use either method please read the all the safety precautions described below. 1. Oven Drying Method: This drying method of silica gel gives the best results even though it takes longer. Set the oven for 120 0C. Place the silica gel in an appropriate container and dry the silica gel until it turns medium blue. The oven drying method takes approximately 1-1/2 hours per quart of silica gel. One quart of silica gel equals weighs approximately 850 grams. 2. Microwave drying method: In this method place the silica gel in an appropriate container and set the microwave power to the medium to medium high setting. Dry silica gel for approximately 3 to 5 minutes and inspect the color change in silica gel crystals. If the silica gel has not dried, stir it with a spoon and heat it for another 3 to 5 minutes. Stir the silica gel mass each time it is inspected. Approximate drying time is 8 to 12 minutes per half kilogram of silica gel. The actual heating times will vary according to the type of microwave. You may set the power setting on high but please be careful not to overheat the silica gel crystals.